Thursday, October 28, 2010

Dino Dung: Paleontology's Next Frontier?

Michael Brett-Surman, a paleontologist at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., notes that coprolites provide a "direct link" to the diets of dinosaurs. (Brett-Surman does not study coprolites, but rather the lives of hadrosaurs, a type of duck-billed dinosaur.)

In a recent interview, Chin even allowed that she is working on a coprolite found to contain fossilized tissuea potentially exciting discovery. (Chin declined to provide more details, citing the protocols surrounding unpublished research.)

Tyrannosaurus Rex Deposit?

Chin, herself, made a big splash in scientific circles in 1998 when she published analysis of a king-sized, meat-eating dinosaur coprolite unearthed in Saskatchewan, Canada. Based on its size (2.4 liters/2.5 quarts), age, the presence of bone chips and other clues, Chin concluded that the most likely candidate to produce such a copious deposit was a Tyrannosaurus rex.

In many respects, Chin's work is akin to forensic pathology. Working in her lab, Chin uses chemical analysis to tease secrets from coprolite samples. Chin often cuts samples into thin slices and examines them under high-powered microscopes. Her early work as a naturalist for the U.S. National Park Service also informs her work, Chin says, noting the variety in moose-dropping consistency she observed throughout seasonal fluctuations of succulent forage.

While investigating the king-sized, Saskatchewan dinosaur coprolite, Chin consulted Greg Erickson, a paleobiologist at Florida State University, who analyzed the vascular patterns found in the bone fragments. Erickson concluded that the prey animal was a sub-adult, plant-eating dinosaur.

In the case of another plant-eating dinosaur coprolite found in Montana's Two Medicine formation, Chin discovered a series of preserved burrows. Consulting with Canadian dung beetle specialist Bruce Gill, Chin confirmed that ancient dung beetles produced the smooth channels.

Grand Synthesis Elusive

Such discoveries may sound like small beer. But they are precisely the type of information that, piece by piece, paper by paper, fossil by fossil, year by year, accumulates into a large database of collective knowledge. Against such a background, a grand synthesis becomes possible on the heels of other discoveries. One recent example is the association of modern birds as the evolutionary descendants of certain dinosaurs.

When it comes to dinosaur coprolites, however, such riveting stories of scientific discovery are few and far between.

The main reason why this is so owes to the fact that coprolites are among the most rare of all dinosaur fossils. "It's easier to find a big, fat diamond then it is to find a coprolite," said Brett-Surman.

"That's why we get so excited when we find dinosaur feces," said Chin.

Part of the problem lies in knowing what to look for when fossil-hunting in the field. Or in the parlance of paleontologists, having the right "search image."

To date, fewer than a dozen coprolite types have been positively linked to dinosaurs. (Compare that to the hundreds of dinosaur species that have been excavated and named over the past 150 years.)

"We only talk about a dozen associations, if that. Given how many dinosaurs we know and how much excavation and exploration we've done, it's rather sad," said Hunt.

Who Dunnit?

Once a coprolite is found, questions mount. Perhaps the most existential: Is the fossil truly a coprolite?

"There a lot of things that people show me that I don't really know," Chin said. "And sometimes, even after tests, I may not be able to tell for sure."

Other cases are more clear; Chin found a patently modern rabbit pellet masquerading as coprolite in one museum collection, according to a previously published profile.

Given the limits of what the fossil record does and does not preserve (what Brett-Surman calls the "great filter of Mother Nature") the most important question surrounding a coprolite is one that often can never be answered. Namely, who produced it?

"In many cases we may never know," said Chin. Or as Brett-Surman said, "Let's put it this way. It's easier to find out what the animal ate then who took the dump."